Effect of two-stage solution on microstructure and mechanical property of IN718 alloy fabricated by selective laser melting

Abstract

The substructure characteristics and mechanical properties of the IN718 alloy prepared via selective laser melting in the as-deposited state and different solid solution states were studied. The effects of the substructure characteristics, which include precipitates and grain boundary features, on the microhardness of the IN718 alloy were investigated. It was found that the main substructure of the as-deposited alloy is a cellular structure, which is formed owing to the 50-nm-thick segregation band of the Nb and Ti elements. The two-stage and single-stage solution processes can both prevent the microsegregation of the as-deposited state, but the two-stage solution process can make the composition more uniform; at the same time, it leads to a large number of twin boundaries. The δ phase precipitates mostly in the single-stage solution process at 980 °C, but the two-stage solution process can effectively inhibit the precipitation of the δ phase. The hardness of the alloy after the two-stage solution process is lower than that of the alloy after the single-stage solution process. The main strengthening mechanism of the as-deposited alloy consists of strain strengthening. The strengthening effect of the δ precipitate is lower than the strain strengthening caused by the grain boundaries of the alloy.

Keywords

• IN718
• two-stage solution
• micro segregation
• grain boundary feature
• selective laser melting